Organs on microfluidic chips: A mini review

An electromechanical stimulation regulating model with flexoelectric effect of piezoelectric laminated micro-beam for cell bionic culture

Cell bionic culture requires the construction of cell growth microenvironments. In this paper, mechanical force and electrical stimulations are applied to the cells cultured on the surface of the piezoelectric laminated micro-beam driven by an excitation voltage. Based on the extended dielectric theory, the electromechanical microenvironment regulating model of the current piezoelectric laminated micro-beam is established. The variational principle is used to obtain the governing equations and boundary conditions. The differential quadrature method and the iterative method are used to solve two boundary value problems for cantilever beams and simply supported beams. In two cases, the mechanical force and electrical stimulations applied to the cells are analyzed in detail and the microscale effect is investigated. This study is meaningful for improving the quality of cell culture and promoting the cross-integration of mechanics and biomedicine.

Organoids/organs-on-a-chip: new frontiers of intestinal pathophysiological models

Organoids/organs-on-a-chip open up new frontiers for basic and clinical research of intestinal diseases. Species-specific differences hinder research on animal models, while organoids are emerging as powerful tools due to self-organization from stem cells and the reproduction of the functional properties in vivo. Organs-on-a-chip is also accelerating the process of faithfully mimicking the intestinal microenvironment. And by combining organoids and organ-on-a-chip technologies, they further are expected to serve as innovative preclinical tools and could outperform traditional cell culture models or animal models in the future. Above all, organoids/organs-on-a-chip with other strategies like genome editing, 3D printing, and organoid biobanks contribute to modeling intestinal homeostasis and disease. Here, the current challenges and future trends in intestinal pathophysiological models will be summarized.

Organoids of the male reproductive system: Challenges, opportunities, and their potential use in fertility research

Organoids are units of function of a given organ able to reproduce, in culture, a biological structure similar in architecture and function to its counterpart in vivo. Today, it is possible to develop an organoid from a fragment of tissue, a stem cell located in an adult organ, an embryonic stem cell, or an induced pluripotent stem cell. In the past decade, many organoids have been developed which mimic stomach, pancreas, liver and brain tissues, optic cups, among many others. Additionally, different male reproductive system organs have already been developed as organoids, including the prostate and testis. These 3D cultures may be of great importance for urological cancer research and have the potential to be used in fertility research for the study of spermatozoa production and maturation, germ cells-somatic cells interactions, and mechanisms of disease. They also provide an accurate preclinical pipeline for drug testing and discovery, as well as for the study of drug resistance. In this work, we revise the current knowledge on organoid technology and its use in healthcare and research, describe the male reproductive system organoids and other biomaterials already developed, and discuss their current application. Finally, we highlight the research gaps, challenges, and opportunities in the field and propose strategies to improve the use of organoids for the study of male infertility situations. This article is categorized under: Reproductive System Diseases > Stem Cells and Development Reproductive System Diseases > Biomedical Engineering.

Real-time monitoring of immediate drug response and adaptation upon repeated treatment in a microfluidic chip system

Microfluidic tissue culture and organ-on-a-chip models provide efficient tools for drug testing in vivo and are considered to become the basis of in vitro test systems to analyze drug response, drug interactions and toxicity to complement and reduce animal testing. A major limitation is the efficient recording of drug action. Here we present an efficient experimental setup that allows long-term cultivation of cells in a microfluidic system in combination with continuous recording of luciferase reporter gene expression. The system combines a sensitive cooled luminescence camera system in combination with a custom build miniaturized incubation chamber. The setup allows to monitor time-dependent activation, but also the end of drug response. Repeated activation and recovery as well as varying durations of drug treatment periods can be monitored, and different modes of drug activity can be visualized.

Design and Fabrication of Organ-on-Chips: Promises and Challenges

The advent of the miniaturization approach has influenced the research trends in almost all disciplines. Bioengineering is one of the fields benefiting from the new possibilities of microfabrication techniques, especially in cell and tissue culture, disease modeling, and drug discovery. The limitations of existing 2D cell culture techniques, the high time and cost requirements, and the considerable failure rates have led to the idea of 3D cell culture environments capable of providing physiologically relevant tissue functions in vitro. Organ-on-chips are microfluidic devices used in this context as a potential alternative to in vivo animal testing to reduce the cost and time required for drug evaluation. This emerging technology contributes significantly to the development of various research areas, including, but not limited to, tissue engineering and drug discovery. However, it also brings many challenges. Further development of the technology requires interdisciplinary studies as some problems are associated with the materials and their manufacturing techniques. Therefore, in this paper, organ-on-chip technologies are presented, focusing on the design and fabrication requirements. Then, state-of-the-art materials and microfabrication techniques are described in detail to show their advantages and also their limitations. A comparison and identification of gaps for current use and further studies are therefore the subject of the final discussion.

Microfluidics and organ-on-a-chip technologies: A systematic review of the methods used to mimic bone marrow

Bone marrow (BM) is an organ responsible for crucial processes in living organs, e. g., hematopoiesis. In recent years, Organ-on-a-Chip (OoC) devices have been used to satisfy the need for in vitro systems that better mimic the phenomena occurring in the BM microenvironment. Given the growing interest in these systems and the diversity of developed devices, an integrative systematic literature review is required. We have performed this review, following the PRISMA method aiming to identify the main characteristics and assess the effectiveness of the devices that were developed to represent the BM. A search was performed in the Scopus, PubMed, Web of Science and Science Direct databases using the keywords (("bone marrow" OR "hematopoietic stem cells" OR "haematopoietic stem cells") AND ("organ in a" OR "lab on a chip" OR "microfluidic" OR "microfluidic*" OR ("bioreactor" AND "microfluidic*"))). Original research articles published between 2009 and 2020 were included in the review, giving a total of 21 papers. The analysis of these papers showed that their main purpose was to study BM cells biology, mimic BM niches, model pathological BM, and run drug assays. Regarding the fabrication protocols, we have observed that polydimethylsiloxane (PDMS) material and soft lithography method were the most commonly used. To reproduce the microenvironment of BM, most devices used the type I collagen and alginate. Peristaltic and syringe pumps were mostly used for device perfusion. Regarding the advantages compared to conventional methods, there were identified three groups of OoC devices: perfused 3D BM; co-cultured 3D BM; and perfused co-cultured 3D BM. Cellular behavior and mimicking their processes and responses were the mostly commonly studied parameters. The results have demonstrated the effectiveness of OoC devices for research purposes compared to conventional cell cultures. Furthermore, the devices have a wide range of applicability and the potential to be explored.

Organs-on-a-Chip Module: A Review from the Development and Applications Perspective

In recent years, ever-increasing scientific knowledge and modern high-tech advancements in micro- and nano-scales fabrication technologies have impacted significantly on various scientific fields. A micro-level approach so-called "microfluidic technology" has rapidly evolved as a powerful tool for numerous applications with special reference to bioengineering and biomedical engineering research. Therefore, a transformative effect has been felt, for instance, in biological sample handling, analyte sensing cell-based assay, tissue engineering, molecular diagnostics, and drug screening, etc. Besides such huge multi-functional potentialities, microfluidic technology also offers the opportunity to mimic different organs to address the complexity of animal-based testing models effectively. The combination of fluid physics along with three-dimensional (3-D) cell compartmentalization has sustained popularity as organ-on-a-chip. In this context, simple humanoid model systems which are important for a wide range of research fields rely on the development of a microfluidic system. The basic idea is to provide an artificial testing subject that resembles the human body in every aspect. For instance, drug testing in the pharma industry is crucial to assure proper function. Development of microfluidic-based technology bridges the gap between in vitro and in vivo models offering new approaches to research in medicine, biology, and pharmacology, among others. This is also because microfluidic-based 3-D niche has enormous potential to accommodate cells/tissues to create a physiologically relevant environment, thus, bridge/fill in the gap between extensively studied animal models and human-based clinical trials. This review highlights principles, fabrication techniques, and recent progress of organs-on-chip research. Herein, we also point out some opportunities for microfluidic technology in the future research which is still infancy to accurately design, address and mimic the in vivo niche.

Controlling Differentiation of Stem Cells for Developing Personalized Organ-on-Chip Platforms

Organ-on-chip (OOC) platforms have attracted attentions of pharmaceutical companies as powerful tools for screening of existing drugs and development of new drug candidates. OOCs have primarily used human cell lines or primary cells to develop biomimetic tissue models. However, the ability of human stem cells in unlimited self-renewal and differentiation into multiple lineages has made them attractive for OOCs. The microfluidic technology has enabled precise control of stem cell differentiation using soluble factors, biophysical cues, and electromagnetic signals. This study discusses different tissue- and organ-on-chip platforms (i.e., skin, brain, blood-brain barrier, bone marrow, heart, liver, lung, tumor, and vascular), with an emphasis on the critical role of stem cells in the synthesis of complex tissues. This study further recaps the design, fabrication, high-throughput performance, and improved functionality of stem-cell-based OOCs, technical challenges, obstacles against implementing their potential applications, and future perspectives related to different experimental platforms.

Cell stretching devices as research tools: engineering and biological considerations

Cells within the human body are subjected to continuous, cyclic mechanical strain caused by various organ functions, movement, and growth. Cells are well known to have the ability to sense and respond to mechanical stimuli. This process is referred to as mechanotransduction. A better understanding of mechanotransduction is of great interest to clinicians and scientists alike to improve clinical diagnosis and understanding of medical pathology. However, the complexity involved in in vivo biological systems creates a need for better in vitro technologies, which can closely mimic the cells' microenvironment using induced mechanical strain. This technology gap motivates the development of cell stretching devices for better understanding of the cell response to mechanical stimuli. This review focuses on the engineering and biological considerations for the development of such cell stretching devices. The paper discusses different types of stretching concepts, major design consideration and biological aspects of cell stretching and provides a perspective for future development in this research area.

Organ-on-a-Chip Systems: Microengineering to Biomimic Living Systems

"Organ-on-a-chip" systems integrate microengineering, microfluidic technologies, and biomimetic principles to create key aspects of living organs faithfully, including critical microarchitecture, spatiotemporal cell-cell interactions, and extracellular microenvironments. This creative platform and its multiorgan integration recapitulating organ-level structures and functions can bring unprecedented benefits to a diversity of applications, such as developing human in vitro models for healthy or diseased organs, enabling the investigation of fundamental mechanisms in disease etiology and organogenesis, benefiting drug development in toxicity screening and target discovery, and potentially serving as replacements for animal testing. Recent advances in novel designs and examples for developing organ-on-a-chip platforms are reviewed. The potential for using this emerging technology in understanding human physiology including mechanical, chemical, and electrical signals with precise spatiotemporal controls are discussed. The current challenges and future directions that need to be pursued for these proof-of-concept studies are also be highlighted.

Investigation of Tumor Cell Behaviors on a Vascular Microenvironment-Mimicking Microfluidic Chip

The extravasation of tumor cells is a key event in tumor metastasis. However, the mechanism underlying tumor cell extravasation remains unknown, mainly hindered by obstacles from the lack of complexity of biological tissues in conventional cell culture, and the costliness and ethical issues of in vivo experiments. Thus, a cheap, time and labor saving, and most of all, vascular microenvironment-mimicking research model is desirable. Herein, we report a microfluidic chip-based tumor extravasation research model which is capable of simultaneously simulating both mechanical and biochemical microenvironments of human vascular systems and analyzing their synergistic effects on the tumor extravasation. Under different mechanical conditions of the vascular system, the tumor cells (HeLa cells) had the highest viability and adhesion activity in the microenvironment of the capillary. The integrity of endothelial cells (ECs) monolayer was destroyed by tumor necrosis factor-α (TNF-α) in a hemodynamic background, which facilitated the tumor cell adhesion, this situation was recovered by the administration of platinum nanoparticles (Pt-NPs). This model bridges the gap between cell culture and animal experiments and is a promising platform for studying tumor behaviors in the vascular system.

3D liver models on a microplatform: well-defined culture, engineering of liver tissue and liver-on-a-chip

The liver, the largest organ in the human body, is a multi-functional organ with diverse metabolic activities that plays a critical role in maintaining the body and sustaining life. Although the liver has excellent regenerative and recuperative properties, damages caused by chronic liver diseases or viral infection may lead to permanent loss of liver functions. Studies of liver disease mechanism have focused on drug screening and liver tissue engineering techniques, including strategies based on in vitro models. However, conventional liver models are plagued by a number of limitations, which have motivated the development of 'liver-on-a-chip' and microplatform-based bioreactors that can provide well-defined microenvironments. Microtechnology is a promising tool for liver tissue engineering and liver system development, as it can mimic the complex in vivo microenvironment and microlevel ultrastructure, by using a small number of human cells under two-dimensional (2D) and three-dimensional (3D) culture conditions. These systems provided by microtechnology allow improved liver-specific functions and can be expanded to encompass diverse 3D culture methods, which are critical for the maintenance of liver functions and recapitulation of the features of the native liver. In this review, we provide an overview of microtechnologies that have been used for liver studies, describe biomimetic technologies for constructing microscale 2D and 3D liver models as well as liver-on-a-chip systems and microscale bioreactors, and introduce applications of liver microtechnology and future trends in the field.

Rational design of a turn-on fluorescent sensor for α-ketoglutaric acid in a microfluidic chip

A rational design of turn-on fluorescent chemosensors for monitoring α-ketoglutaric acid has been developed with a microfluidic chip, indicative of a potential platform for high-throughput screening and monitoring of kinetics, especially in biological fields.